1. Technical Field
The present invention relates to a process for producing an emissive device and also relates to an emissive device and an electronic apparatus.
2. Related Art
Organic electroluminescent (EL) elements each including an emissive organic layer (organic electroluminescent layer) disposed between a cathode and an anode can achieve significantly low applied voltages compared with inorganic electroluminescent elements. Furthermore, organic EL elements that display various colors can be produced.
Specifically, organic EL elements each include an anode, a cathode, and an organic EL layer disposed between the anode and the cathode.
In general, organic EL layers are each composed of three layers, i.e., a hole transport layer, an emissive layer, an electron transport layer, and, optionally, other layers.
In organic EL elements, various methods, such as an RGB separate deposition method, a color filter method, and a color conversion method, are known as a method for displaying colors.
An organic EL element according to the RGB separate deposition method includes emissive layers that display three colors, red (R), green (G), and blue (B), the emissive layers being disposed separately from each other in a single pixel. Independent control of the emission of each emissive layer results full-color emission.
Such R-, G-, and B-emissive layers are generally formed by vacuum evaporation with emissive materials. For example, Japanese Unexamined Patent Application Publication Nos. 2000-91082 and 8-227276 each disclose a method for forming emissive layers through three evaporation steps with three types of masks in such a manner that each emissive layer is deposited on a predetermined region by vacuum evaporation.
In recent years, there have been advances in the development of full-color organic EL elements according to an RGBW separate deposition method in order to suppress the degradation of the emissive layers.
Organic EL elements according to the method for displaying colors each include emissive layers that display four colors, R, G, B, and white (W), in a single pixel. Among the emissive layers displaying four colors, the emissive layer displaying W is formed by overlapping at least two emissive layers of the emissive layers displaying R, G, and B.
Such an organic EL element may be formed by a method, similar to the above-described method, of forming emissive layers displaying R, G, and B, preparing a mask for forming an emissive layer displaying W, successively depositing at least two emissive layers of the emissive layers displaying R, G, and B with the mask to form the emissive layer displaying W.
In the method, at least four types of masks and at least five evaporation steps are required to form the emissive layers displaying the four colors. However, in view of economics, it is intended to minimize the number of the masks used because the masks are significantly expensive.
The evaporation steps are performed in reduced pressure for a prolonged period of time, thus prolonging the production process of the organic EL element.